The term “field device” collectively refers to such measuring instruments as various flowmeters, temperature measuring instruments, and pressure measuring instruments, and also refers to control instruments, valves, and the like, which are mainly used in, for example, plant facilities or factory facilities, regardless of indoors or outdoors.
As a typical field device, there exists a flowmeter for measuring the flow rate of a fluid flowing through a pipe of a plant, or a batch counter (pre-set counter) for controlling, with a combination of a flowmeter and a valve, the operation of the valve based on a flow rate signal from the flowmeter.
Further, many of those instruments are provided with a display portion or an operation portion for making various settings through a view of the display portion.
Examples of the flowmeter, which is one kind of the field device, include a positive displacement flowmeter and a Coriolis flowmeter. The positive displacement flowmeter generally includes a measuring chamber having a rotor, which rotates in proportion to the volume of a fluid to be measured flowing through a flow tube, provided therein, and determines the flow rate based on the rotation of the rotor rotating in proportion to the volume of the fluid to be measured flowing into the measuring chamber. The Coriolis flowmeter is a mass flowmeter in which one end or both ends of a flow tube through which a fluid to be measured is flowing are supported, and which utilizes a fact that a mass flow rate is proportional to a Coriolis force acting on the flow tube (which is a tube in which oscillation is to be generated) when oscillation is generated in a direction perpendicular to a flow direction of the flow tube with the supported points being fixed.
The positive displacement flowmeter is commonly known as in the technology disclosed in, for example, JP 3529201 B2. Further, the Coriolis flowmeter, which is a mass flowmeter, is commonly known as in the technology disclosed in, for example, JP 2005-221251 A.
The positive displacement flowmeter disclosed in JP 3529201 B2 has a counter built in a casing structured by a casing main body and a cover. The casing is separately structured from the counter. The flow rate calculated by the counter is displayed as a numerical value on an LCD indicator provided to the counter. The flow rate displayed on the LCD indicator can be visually recognized through a window of the cover.
When or after the positive displacement flowmeter is mounted to a predetermined position of a pipe, the direction of the counter is adjusted so that the front surface of the counter (specifically, the front surface of the counter housing) can be viewed from the upright direction of the front surface. When the positive displacement flowmeter disclosed in JP 3529201 B2 is mounted, the adjustment is performed as well so that the front surface of the counter can be viewed from the upright direction thereof through the window of the cover.
Further, as is widely known, the Coriolis flowmeter is amass flowmeter in which one end or both ends of a flow tube through which a fluid to be measured is flowing are supported, and which utilizes the fact that a mass flow rate is proportional to a Coriolis force acting on the flow tube (which is a tube in which oscillation is to be generated) when oscillation is generated in a direction perpendicular to a flow direction of the flow tube with the supported points being fixed. The shape of the flow tube in the Coriolis flowmeter is classified into two major types of a straight tube type and a U-shaped tube type.
As described above, the Coriolis flowmeter is amass flowmeter in which a flow tube, through which a fluid to be measured flows, is supported at both ends thereof, and when a central portion of the supported flow tube is alternately driven in a direction perpendicular to a support line, a phase difference signal proportional to a mass flow rate is detected between the supported portions positioned at symmetric positions of the flow tube at its both ends with respect to the central portion.
Then, when the frequency for alternately driving the flow tube is made equal to the eigen frequency of the flow tube, a constant drive frequency can be obtained according to the density of the fluid to be measured, which enables driving the flow tube with small drive energy. Accordingly, in recent years, it has been a common practice to drive the flow tube at the eigen frequency. The phase difference signal is proportional to the mass flow rate, but assuming that a drive frequency is constant, the phase difference signal can be detected as a time difference signal between observation positions of the flow tube.
In recent years, the field device has been provided with a feature that the settings thereof can be changed on the spot through touch operation.
With the provision of a non-contact switching device (SW) employing photoelectric sensing, the setting operation for the field device is performed on the spot through the touch operation on a light-emitter-beam transmissive material (for example, glass).
The principle of an optical switch, which is a non-contact switching device (SW) employing optical sensing, is as follows. That is, the optical switch performs switching (SW operation) by being turned on or off when light emitted from a light emitter such as an LED has been received by a photodetector such as a commercially available photo IC, or being turned off or on when light emitted from the light emitter such as an LED has ceased to be received by the photodetector such as a photo IC.
The non-contact switching device (SW) described above generally has such a configuration as illustrated in FIG. 11. Specifically, a non-contact switching device (SW) 500 includes a light emitter (for example, LED) 510 and a photodetector (for example, commercially available photo IC) 520, and the light emitter (for example, LED) 510 and the photodetector (for example, photo IC) 520 are each surrounded by a light blocking structure 530. The light emitter (for example, LED) 510 and the photodetector (for example, photo IC) 520 are disposed in an isolated manner so that light emitted from the light emitter (for example, LED) 510 does not directly enter the photodetector (for example, photo IC) 520.
Above the light emitter (for example, LED) 510 surrounded by the light blocking structure 530, there is formed an opening 531 so that light emitted from the light emitter (for example, LED) 510 is emitted upward from inside the light blocking structure 530. Further, above the photodetector (for example, photo IC) 520 surrounded by the light blocking structure 530, there is formed an opening 532 so that the light emitted from the light emitter (for example, LED) 510 enters the light blocking structure 530 from a predetermined direction after being reflected by a light reflector.
A top side of the light blocking structure 530 is covered with a light-emitter-beam transmissive material (for example, glass) 540. Thus, the light-emitter-beam transmissive material (for example, glass) 540 serves as a top cover of the light blocking structure 530, and corresponds to a glass cover portion of a setting device portion of a housing of the field device.
In the optical switch 500 having the above-mentioned configuration, light is constantly emitted from the light emitter (for example, LED) 510, and the light emitted from the light emitter (for example, LED) 510 is emitted from the opening 531 formed above the light blocking structure 530. Further, the photodetector (for example, photo IC) 520 is capable of constantly receiving the incident light from the opening 532 formed above the light blocking structure 530.
In such a state, when a light reflector (detection object) 550, such as a finger, is put over the light-emitter-beam transmissive material (for example, glass) 540, the light emitted from the light emitter (for example, LED) 510 and then from the opening 531 formed above the light blocking structure 530 is reflected by the light reflector (detection object) 550, such as a finger, which has been put over the light-emitter-beam transmissive material (for example, glass) 540, and is then caused to enter the opening 532 formed above the light blocking structure 530, with the result that the light is received by the photodetector (for example, photoreflector) 520.
With this, the switch is turned on. This switch on enables the settings or the like of the field device to be changed.
Specifically, the light emitter (for example, LED) 510 is installed with an emitting angle thereof set so that, when the light reflector (detection object) 550, such as a finger, is put over the light-emitter-beam transmissive material (for example, glass) 540, the light emitted from the light emitter (for example, LED) 510 and then from the opening 531 formed above the light blocking structure 530 is reflected by the light reflector (detection object) 550, such as a finger, and is then caused to enter through the opening 532 formed above the light blocking structure 530.
Further, the photodetector (for example, photo IC) 520 is installed with a receiving angle thereof set so that the light emitted from the light emitter (for example, LED) 510 is received after entering through the opening 532 formed above the light blocking structure 530.
Regarding such a non-contact switching device (SW) employing the photoelectric sensing, a general optical signal switching device is described in JP 2006-234526 A. JP 2006-234526 A describes an optical signal switching device which can easily set a detection distance of reflection of a light receiving element, and can prevent a malfunction. Further, with regard to the optical signal switching device of Patent Document 3, there is a description about a sensitivity adjusting circuit 22 which adjusts the detection sensitivity for a reflected wave from the light receiving element 16.